This invention relates to a non-aqueous electrolytic solution secondary cell, and in more detail to such cell using an electrolytic solution containing a specific aromatic carbonate. The cell of the present invention is successful in suppressing decomposition of the electrolytic solution, and achieving a high capacity and excellent cycle characteristics, and thus can allow down sizing and improvement in performances of the non-aqueous electrolytic solution secondary cell.
Along with recent trends in weight and size reductions of electric appliances, attention to lithium secondary cell has been growing due to its high energy density. There are also requirements for improved cell characteristics as applications of lithium secondary cell spread.
A secondary lithium cell having a metal lithium negative electrode has a long history of extensive studies expected for providing a high energy density. The cell, however, suffers from a technical problem in that metal lithium is likely to grow up to form dendrite on the surface of the negative electrode after repetitive charge/discharge cycles, and the dendrite can finally reach the positive electrode to thereby cause short-circuit failure, which is a largest obstacle to the practical use thereof.
There is proposed a non-aqueous electrolytic solution secondary cell employing as a negative electrode material a carbonaceous material, such as coke, artificial graphite or natural graphite, which is capable of occluding or liberating lithium ion. Such non-aqueous secondary cell is successful in that the growth of the dendrite is fully controlled and thereby the lifetime and safety of the cell improves, since lithium does not present in a form of solid metal state.
The negative electrode made of a carbonaceous material is generally obtained by dispersing carbon powder material and optional conductive material (e.g., carbon black, acetylene black) into a binder to thereby prepare a slurry, coating the obtained slurry onto a current collector, and drying the coated film. The binder employed herein may be a variety of known substances such as polyvinylidene fluoride and poly(tetrafluoroethylene), where polyvinylidene fluoride is most popular due to its excellent chemical stability and convenience in electrode production.
On the other hand, as for a solvent for the electrolytic solution of such lithium secondary cell, non-aqueous organic solvents generally used include carbonates such as ethylene carbonate, propylene carbonate and diethyl carbonate; and esters such as xcex3-butyrolactone. A problem of decomposition of the electrolytic solution is, however, inevitable in the lithium secondary cell despite a relatively high stability of the foregoing solvents contained in such electrolytic solution, since the cell has an operational potential range of as large as 3 V or above and uses a highly active lithium. This tends to result in degraded charge-discharge efficiency and cycle characteristics.
It is therefore an object of the present invention to provide a non-aqueous electrolytic solution secondary cell minimizing the decomposition of the electrolytic solution and thus achieving excellent cycle characteristics and energy density, and in particular achieving a high maintenance factor of the discharge capacity.
The inventors of the present invention found out, after extensive investigations to accomplish the foregoing object, that using an electrolytic solution containing a specific kind of aromatic carbonate can successfully provide a non-aqueous electrolytic solution secondary cell with excellent characteristics and high energy density, which led us to propose the present invention.
That is, the present invention is to provide a non-aqueous electrolytic solution secondary cell comprising a negative electrode containing a carbonaceous material capable of occluding and liberating lithium, a positive electrode, a non-aqueous electrolytic solution which includes a solute and an organic solvent, and a separator;
wherein the organic solvent contains at least one of compounds selected from those expressed by the formulae (I) and (II) below: 
(in which xcfx86 represents a phenyl group optionally having an alkyl group; and R represents any one of a hydrogen atom, C1-4 alkyl groups and a phenyl group optionally having an alkyl group).